The benefits of caching systems are well known. Local client-based browser caches may cache for one user and/or for one computer. Shared caching systems may cache content for multiple users, such as multiple web users, and/or multiple computers. For web page servers, shared caching systems may save the server from having to deliver content directly to each client. However, most shared caching systems rely on a time-based caching approach. A time duration is established for how long cached web pages can be relied upon with assurance to be current, and the established time duration is used to determine a time that web pages remain available in cache. For web page or other content servers with content that changes frequently, the benefits of caching may be rather small, as the cached versions of the web pages are expired from cache quickly.